Biochemical evidence of animal evolution

T

he world of living things, the origins of the species that make it up, their links through the millennia, what different organisms are made of - these are questions that have intrigued human beings for centuries. Some ancient philosophers would have approached the phenomenon of evolution, but it wasn't until the 19th century that scientific explanations were commonly accepted. Charles Darwin's theory, published in "The Origin of Species" in 1859, postulates that all living species have evolved from one or a few common ancestors through the process of natural selection. This approach to the living world explains the origin of biodiversity on Earth.

At the same time, but a few years earlier, Theodor Schwann, professor at the University of Liège, proposed his cell theory, according to which the cell is the origin of life and represents the basic unit in biology. This work of thought subsequently led to the advent of cytology, the study of isolated cells.

Years later, in the early 1900s, another scientist from the University of Liège, Marcel Florkin, used these two theories to analyze the living world at the level of biochemical compounds.

Analogous or homologous proteins?

" Marcel Florkin is the father of comparative biochemistry," says Vincent Geenen, Professor of Embryology at the University of Liège. " In 1944, he published "Evolution biochimique" (1), which was translated into several languages, including English, Italian and Russian. In this work, he laid the foundations for the search for the traces of evolution that can be discovered through biochemistry ". Marcel Florkin began his research as a psychiatric intern at the end of his medical studies. " He was convinced that mental illness stemmed from biochemical disturbances. By this time, he was already spending his free time in the laboratory. Following in the footsteps of Léon Fredericq, he worked on cross-species oxygen transporters. His animal model of choice was the silkworm. He feeds these invertebrates from the mulberry tree planted by Léon Fredericq in the garden of the Physiology Institute. In " Evolution biologique ", Marcel Florkin introduces, among other things, an important concept: the distinction between homology and analogy. Proteins are homologous if they are related, derived from a common ancestral precursor. Analogous proteins have evolved to perform the same functions, but are not related. " In his research on oxygen transporters, Marcel Florkin demonstrated that hemocyanin, used by a large number of invertebrates, and hemoglobin, an oxygen transporter in vertebrates, are analogous because they perform the same function without any biochemical kinship," explains Vincent Geenen.

A biochemical unit of life

In his book on biochemical evolution, Marcel Florkin highlights the similarity between the organic and inorganic chemical composition of living beings. He shows that there is, in fact, a certain homogeneity in the composition of proteins, lipids and carbohydrates, and that inorganic elements such as chlorine ions, sulfates, etc. are constantly present. Here's an excerpt from his book on the subject: " In short, we observe throughout the animal series a fundamental chemical plan that is common to all its members: the body is always constituted for its predominant mass by water. In the dry residue, the largest portion of constituents is always formed by a mixture of carbohydrates, lipids and protids, and the inorganic portion is always predominantly constituted by chlorides, sulfates, phosphates and bicarbonates of sodium, potassium, calcium and magnesium ". In much the same way as Theodor Schwann revealed the cell as a biological unit, Marcel Florkin revealed the existence of a biochemical unity of living organisms. " His work in unifying the living through the world of biochemistry is universally known," says Vincent Geenen. To reveal this biochemical unity of animal life, Marcel Florkin used the classical methods of detection and assay of biochemical compounds used at the beginning of the 20th century, such as colorimetric and gravimetric assays.

Scholar and winner of the Prix Francqui

In the course of his research, Marcel Florkin paid particular attention to other processes and mechanisms common to all living beings. " He noticed that muscle contraction, in both vertebrates and invertebrates, combines two mechanisms of action: the breakdown of glycogen and the action of myosin. The former provides glucose for energy, while the latter is responsible for contractility," explains Vincent Geenen. In his book " Evolution biochimique ", Marcel Florkin also talks a lot about oxidative phosphorylation. This process takes place in the mitochondria during the cell's respiratory chain. Put simply, this complex process generates energy for the cell via the transmission of phosphate. " This law is still universal today," explains Vincent Geenen. Geenen himself has been confronted with questions of biochemical evolution in the course of his research. " In particular, during a study on the hypothesis of new members of the neurohypophyseal hormone family. We have written this article in memory of Marcel Florkin ".

A great scholar and friend of Nobel Prize winner Christian de Duve, Marcel Florkin loved to write. " He edited 34 volumes of Comprehensive Biochemistry, the 30th of which he wrote in its entirety, and which is dedicated to the history of biochemistry ", says Vincent Geenen. He was also passionate about writing history books on the great figures of science in Liège. Finally, he also wrote " Biochimie et Biologie moléculaire " (2) in 1966, which for years was the reference syllabus in biochemistry for students at the University of Liège.

In 1946, Marcel Florkin's work was rewarded with the prestigious Prix Francqui, also known as the Belgian Nobel Prize. The man who declared " my sole purpose is to identify in the biochemical order the evidence of animal evolution " has left his mark on the evolution of scientific knowledge!

Written by Audrey Binet

(1) Biochemical evolution. Desoer (Liège), 1944.

(2) Biochemistry and molecular biology. Desoer (Liège), 1966 (1e édition) - with Ernest Schoffeniels.

See Marcel Florkin's biography

Colorimetric assay: type of assay possible when a chemical reaction produces colored products and the intensity of the coloration is proportional to the concentration of the element being assayed.

Gravimetric determination: analytical method using mass. The principle is to chemically react the ion, element or compound whose content is to be determined in the sample. Depending on the case, it may be the mass of the product or the difference in mass of the sample which, after calculation, will determine the content or nature of the product.

Mitochondria: Intracellular structure (or organelle) measuring around one micron, within which the energy produced by organic molecules is recovered and stored before being used by the cells.